Hydroformylation/imine/enamine formation

Scheme 11 Basic principle for imine and enamine formation under hydroformylation conditions...

Abstract Aldehydes obtained from olefins under hydroformylation conditions can be converted to more complex reaction products in one-pot reaction sequences. These involve heterofunctionalization of aldehydes to form acetals, aminals, imines and enamines, including reduction products of the latter in an overall hydroaminomethylation. Furthermore, numerous conversions of oxo aldehydes with additional C.C-bond formation are conceivable such as aldol reactions, allylations, carbonyl olefinations, ene reactions and electrophilic aromatic substitutions, including Fischer indole syntheses. 

Similar to the formation of AT.A/ -acetals under hydroformylation conditions attack of the carbonyl carbon by primary or secondary amines can lead to imines and enamines, respectively (Scheme 11). 

Intermolecular and intramolecular HAMs are known. The transformation can be considered as a tandem reaction [2,3] consisting of three consecutive steps (i) hydroformylation, (ii) formation of an imine or an enamine, and (iii) reduction. Finally, the Af-alkylated amine is produced [4]. Clearly, these reactions can also be carried out in separate steps, but the application of uniform reaction conditions offers considerable advantages, such as the use of a single catalyst for the hydroformylation and the hydrogenation steps. Moreover, the equihbrium of the formation of the intermediate imine or enamine can be advantageously shifted by the irreversible hydrogenation in the last step [5]. 

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